>Why do you pop the keyframes context here?

To preserve correct indentation.
Add code below in editor ``Ctrl-A`` => ``Tab`` => ``Ctrl-Tab``.
When ``Ctrl-A`` => ``Tab`` => ``Ctrl-Tab`` is done Without ``popContext(state)`` the indentation after the closing ``keyframes`` bracket``}`` is incorrect.

````css
h1 {
  animation-duration: 3s;
  animation-name: slidein;
}

@keyframes slidein {
  from {
    margin-left: 100%;
    width: 300%; 
  }

  to {
    margin-left: 0%;
    width: 100%;
  }
}

/* Some example CSS */

@import url("something.css");

body {
  margin: 0;
  padding: 3em 6em;
  font-family: tahoma, arial, sans-serif;
  color: #000;
}

#navigation a {
  font-weight: bold;
  text-decoration: none !important;
}

h1 {
  font-size: 2.5em;
}

h2 {
  font-size: 1.7em;
}

h1:before, h2:before {
  content: "::";
}

code {
  font-family: courier, monospace;
  font-size: 80%;
  color: #418A8A;
}
````